An operational transconductance amplifier (OTA) is a circuit that produces an output current proportional to a differential input voltage. The ratio of the output current to the input voltage is the transconductance, g.sub.m, of the amplifier. OTAs may have different values of g.sub.m suited for different applications. Also, the output signal (current) amplitude may be tailored to suit a particular application.
OTAs have many applications including telecommunications. For example, OTAs are used for providing functions such as baseband filtering or signal level regulation. A complex telecommunications circuit may include many OTAs configured to provide a variety of functions.
Other applications for OTAs include portable telecommunications products, such as radiotelephone handsets. A radiotelephone handset is a portable radio that may communicate with one or more radiotelephone base stations according to a predetermined telecommunications protocol. Electrical power for the radiotelephone handset is provided by a battery.
Radiotelephone handsets are typically designed to be physically small in size and with minimal power dissipation to increase battery life. These design goals enhance the portability of the handset.
To reduce handset size, the circuitry that provides the handset's functionality is constructed using highly integrated circuits. Typical integrated circuit fabrication processes provide bipolar and field effect transistors, resistors, capacitors and other circuit elements. These elements are combined to provide higher levels of functionality, such as amplification stages, current sources, etc.
To reduce power dissipation, static and dynamic currents in the radiotelephone handset control circuitry are reduced. Static currents may include active current sources used to establish voltage and other levels in the circuit. Generally, the extent to which static current levels may be reduced is limited by performance requirements of the circuit. For example, in an OTA, operational parameters such as frequency response and peak output signal amplitude may be reduced to unacceptable levels as static current levels are reduced.
Therefore, there is a need for an operational transconductance amplifier circuit having reduced current drain relative to prior art operational transconductance amplifier circuits but without a reduction in performance parameters. Further, there is a need for such an operational transconductance amplifier circuit suitable for use with a radiotelephone handset.